Consultations through interpreters in the medical outpatient department of a Nigerian hospital were tape-recorded. These recordings were translated completely into English and transcribed, and the performance of the interpreters was analysed. The interpreters often did not provide word-for-word translations of what the doctor or patient had said. Some of these deviations were helpful, but others were confusing or incorrect. In particular, interpreters were inclined to conduct much of the consultations themselves. Hospitals using interpreters should ensure that they have no conflicting duties during consultations and that they have some training in language and interpretation. The quality of interpretation should be checked by native-speaking doctors and by using recordings. Doctors using interpreters should try to make sure that everything said is translated and check the patient's answers by asking questions in several ways.